Your engine has carboned up through general use and your cat is probably filthy.
Two options- new cat or a terraclean.
Search the web for terraclean challenge to see if you have a garage nearby that provides this service.
You may find it costs up to £100 but you'll definitely pass your emissions after.

I did take ht leads of and in the chambers it was full of oil. Coupke of months ago i left the oil cap off so presume it filled then cleaned it and its running better now. Do u think that would have skewed emmissions?